Method for dressing grinding wheels

ABSTRACT

An improved method for dressing the periphery of a grinding wheel having a circular main surface which extends transversely to a circular shoulder. To dress the main surface of the grinding wheel, an axially extending surface on a first dressing wheel is moved into engagement with the main surface of the grinding wheel. To dress the shoulder surface, an axially extending surface on a second dressing wheel is moved into engagement with the shoulder surface of the grinding wheel. The two dressing wheels are mounted on a common carriage or slide which is moved relative to the grinding wheel by a three-position motor assembly. The three-position motor assembly and dressing wheel slide are both mounted on a base slide which is moved toward and away from the grinding wheel by another motor. The two dressing wheels are mounted for rotation about transversely extending axes and are positioned relative to each other in such a manner that when the first dressing wheel is in engagement with the main surface of the grinding wheel, the second dressing wheel is spaced from the shoulder surface of the grinding wheel. Similarly, when the second dressing wheel is in engagement with the shoulder surface of the grinding wheel, the first dressing wheel is spaced from the main surface of the grinding wheel.

United States Patent Messier Nov. 4, 1975 METHOD FOR DRESSING GRINDING[57] ABSTRACT WHEELS An improved method for dressing the periphery of a[75] Inventor: Francis L. Me sie Worcester, grinding wheel having acircular main surface which Mass. extends transversely to a circularshoulder. To dress the main surface of the 'ndin wheel, an axiall ex-[73] Asslgnee: The Warner swasey Company tending surface on a first dressi g wheel is moved into Cleveland Ohm engagement with the mainsurface of the grinding [22] Filed: Nov. 29, 1973 wheel. To dress theshoulder surface, an axially extendin surface on a second dressin wheelis moved [21] Appl' 419997 into eigagement with the shoulde surface ofthe grinding wheel. The two dressing wheels are mounted [52] US. Cl.51/283; 125/11 CD on a common c g or slide which is moved relative [51]Int. Cl. B24B 1/00 t the g n ng e l y a thr -p sition m tor ass m- [58]Field of Search 125/11 R, 11 CD; 51/5, y- The three-position m r em y nr ing 51/105 SP 283 wheel slide are both mounted on a base slide whichis moved toward and away from the grinding wheel by [56] References Citd another motor. The two dressing wheels are mounted UNITED STATESPATENTS for rotation about transversely extending axes and are 3 407 80010/1968 Home 125,11 R positioned relative to each other in such a mannerthat 3553893 H1971 Sta 51 /5 D when the first dressing wheel s inengagement with 3:581:730 6/1971 Boyd "fig CD the main surface :of thegrinding wheel, the second 3,678,916 7,1972 Fujii 125,11 CD dressingwheel IS spaced from the shoulder surface of 3,633,385 8/1972 Kikuchi N125/11 CD the grinding wheel. Similarly, when the second dress-3,747,5s4 7 1973 Kikuchi 125/11 co ing wheel is in engagement with theshoulder surface 3,822,689 7/1974 Oshima 125/11 DF X of the grindingwheel, the first dressing wheel is Primary ExaminerHarold D. Whiteheadspaced from the main surface of the grinding wheel.

5 Claim, 12 Drawing Figures U.S. Patent Nov. 4, 1975 Sheet 1 of4 3,916,581

US. Patent Nov. 4, 1975 Sheet 2 of4 3,916,581

WMQ

US. Patent Nov. 4, 1975 Sheet 3 of4 3,916,581

as 26 9o FTE. 5

U.S. Patent Nov. 4, 1975 Sheet4 0f4 3,916,581

METHOD FOR DRESSING GRINDING WHEELS BACKGROUND OF THE INVENTION Thisinvention relates to an improved method and apparatus for dressing theperiphery of a grinding wheel having a circular main surface and acircular shoulder surface which extends transversely to the mainsurface.

Grinding wheels which are utilized to finish parts 0 utilized to finisha radially extending surface on the part.

A known dressing wheel having a cylindrical surface is utilized to dressthe main surface of'the grinding wheel. A radially extending surface ofthe known dressing wheel is utilized to dress the shoulder surface ofthe grinding wheel. The relatively large contact area between, theshoulder surface of the grinding wheel and the radially extendingsurface of the dressing wheel requires the application of relativelylarge forces to dress the wheel. In an effort to oyercome the problemsresulting from the utilization of such a dressing wheel, it has beensuggested to utilize a dressing wheel which is rotatable upon an axiswhich is different from the axis about which the workpiece is rotatedand which has frustro-conical dressing surfaces in the manner disclosedin U.S. Pat. No. 3,526,058.

SUMMARY OF THE PRESENT INVENTION The present invention provides animproved method for dressing the periphery of a grinding wheel having acircular main surface and a circular shoulder surface extendingtransversely to the main surface by utilizing different dressing wheelsto dress these two surfaces. Thus, a first or main dressing wheel isutilized to dress the main surface of the grinding wheel. -A second orshoulder dressing wheel is utilized to dress a shoulder surface of thegrinding wheel. By utilizing separate dressing wheels to dress thesurfaces of the grinding wheel, the contact area between each of thesurfaces of the grinding wheel and the two dressing wheels is minimizedto tend to optimize the finish obtained on the surfaces of the grindingwheel with the application of relatively low forces to the dressingwheels.

The two dressing wheels may be mounted on a common slide or carriage androtated about transversely extending axes. The common carriage isadvantageously moved by a three-position motor assembly. Upon operationof this motor assembly from a retracted condition to a first extendedcondition the main or first grinding wheel is moved axially alonga pathextending parallel to the main surface of the grinding wheel. Uponoperation of the'motor assembly to a second extended position, anaxially extending outer surface of the second or shoulder dressing wheelis moved radially into engagement with the shoulder surface of thegrinding wheel.

Accordingly, it is an object of this invention to provide a new andimproved method for dressing the periphery of a grinding wheel having acircular main surface and acircular shoulder surface by engaging themain surface of the grinding wheel with a first dressing 2 wheel andengaging the shoulder surface of the grinding wheel with a seconddressing wheel.

. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects andfeatures of the present invention will become more apparent upon a vconsideration of the following description taken in con:

nection with the accompanying drawings wherein:

FIG. 1 is a plan view of a grinding machine having a wheel dressingarrangement which is constructed and operated in accordance with thepresent invention, a main dressing wheel being shown in engagement witha main surface of the grinding wheel;

FIG. 2 is an elevational view, taken generally along.

the line 2-2 of FIG. 1, and illustrating the relationship between ashoulder dressing wheel, the main dressing wheel, and a carriage orslide on which the dressing wheels are rotatably mounted; FIG. 3 is anenlarged, partially schematized illustration depicting the relationshipbetween a three-position motor assembly and control valves for effectingoperation of the motor assembly to move the dressing wheel slide, themotor assembly being shown in a retracted condition;

FIG. 4 is an illustration of the motor assembly of FIG. 3 in a partiallyextended condition in which the main dressing wheel engages the mainsurface of the grinding wheel; 7 FIG. 5 is an illustration of the motorassembly of FIGS. 3 and 4 in a fully extended condition in which theshoulder dressing wheel engages a shoulder surface of the grindingwheel;

FIG. 6 is a schematic illustration depicting the relationship betweenthe main and shoulder dressing wheels when they are in an initialretracted condition; FIG. 7 is a schematic illustration of the dressingof the main surface of the grinding wheel; FIG. 8 is a schematicillustration depicting the relationship between the main dressing wheeland the grinding wheel at the end of a wiping stroke across the mainsurface of the grinding wheel;

FIG. 9 is a schematic illustration depicting the mai and shoulderdressing wheels in the retracted condition after completion of thewiping stroke;

FIG. 10 is a schematic illustration depicting the dressing of theshoulder surface of the grinding wheel; FIG. 11 is a schematicillustration depicting the main and shoulder dressing wheels in theretracted condition upon completion of a dressing operation; and,

FIG. 12 is a schematic illustration of control circuitry associated withthe motor assembly and control apparatus of FIG. 3.

DESCRIPTION OF ONE SPECIFIC PREFERRED EMBODIMENT OF THE INVENTION Agrinding machine 20 is illustrated in FIG. I and includes a wheeldressing apparatus 22 which is constructed and operated in accordancewith the present invention to dress a main surface 24 and shouldersurface 26 of a grinding wheel 28. The wheel dressing apparatus 22includes a first or main dressing wheel 32 which is utilized to dressthe main surface 24 of the grinding wheel 28 and a second orshoulderdressing wheel 34 which is utilized to dress the shoulder surface 26 ofthe grinding wheel. The two dressing wheels 32 and 34 are rotatablymounted on a common slide or carriage 38 which is movable relative to abase slide 40 by a three-position motor assembly 42. The base slide 3 40is movable relative to a base or bed 44 of the grinding machine by apiston and cylinder type motor 46 (illustrated schematically in FIG. 1)to position dressing wheels 32 and 34 along a path extendingperpendicular to an axis 48 of rotation of the grinding wheel 28.

When the transversely extending main and shoulder surfaces 24 and 26 ofthe grinding wheel 28 are to be dressed, the main surface is dressed bythe wheel 32 before the shoulder surface is dressed by the wheel 34. Todress the main surface 24, the main dressing wheel 32 is moved from theretracted position of FIG. 6 to the operating position of FIG. 7 underthe combined influence of the three-position motor assembly 42 and thebase slide motor 46. The base slide motor 46 is activated to move thedressing wheel 32 sidewardly toward the grinding wheel 28.contemporaneously therewith, the three-position motor assembly 42 isoperated from the initial or retracted condition of FIG. 3 to thepartially extended condition of FIGS. 1 and 4 to shift the wheel slide38 and move the main dressing wheel 32 axially relative to the main orface surface 24 of the grinding wheel 28.

Before a cylindrical outer surface 52 of the dressing wheel 32 is movedinto engagement with the main surface '24 of the grinding wheel 28, thedressing wheel 32 is brought up to a predetermined rotational speed by adrive arrangement which includes a sheave 56 which is driven by suitablebelts 58. Of course, the grinding wheel 28 is also rotated about itscentral axis 48 by a suitable drive arrangement. As the grinding wheel28 and main dressing wheel 32 are rotated, the main surface 24 of thegrinding wheel is dressed in a known manner. It should be noted that theshoulder dressing wheel 32 is spaced from the shoulder surface 26 of thegrinding wheel 28 while the main surface 24 is to be dressed.

When the main surface 24 of the grinding wheel 28 has been dressed to adesired surface finish, the motor assembly 42 is operated to shift thedressing wheel 32 axially from the position shown in FIG. 7 to theposition shown in FIG. 8 to wipe the main surface 24 of the dressingwheel 28. This is accomplished by operating the motor assembly 42 fromthe partially extended condition of FIG. 4 to the retracted condition ofFIG. 3. As this occurs the dressing wheel slide 38 (FIG. 1) is shiftedalong a path extending parallel to the main surface 24 of the grindingwheel 28 to move the cylindrical outer surface 52 of the dressing wheel32 axially along the main surface of the grinding wheel to thereby wipethe main surface of the grinding wheel in a known manner.

Once the main surface 24 of the grinding wheel 26 has been dressed, theshoulder surface 26 of the grinding wheel is dressed by the dressingwheel 34. Upon completion of the wiping stroke of the main dressingwheel 32, the main dressing wheel and shoulder dressing wheel 34 areshifted from the positions shown in FIG. 8 to the retracted positions ofFIG. 9. This is accomplished by operating the base slide motor 46(FIG. 1) to move the base slide 40 and the dressing wheel slide 38 awayfrom the grinding wheel 28. As this occurs, the shoulder dressing wheel34 is moved into radial alignment with the shoulder surface 26 of thegrinding wheel 28 (see FIG. 9).

The three-position motor assembly 42 is then operated from the retractedcondition to FIG. 3 to a second operating or fully extended condition ofFIG. 5. This moves the shoulder dressing wheel 34 radially toward theshoulder surface 26 along the path extending perpendicular to theshoulder surface 26. As this occurs, a cylindrical outer surface 64 onthe shoulder dressing wheel 34 moves into abutting engagement with theshoulder surface 26 on the grinding wheel 28.,It should be noted thatthe main dressing wheel 32 is spaced apart from the grinding wheel 28and is disposed axially to the left (as viewed in FIGS. 611) of the mainsurface grinding position of FIG. 7 when the shoulder dressing wheel 34engages the grinding wheel.

The shoulder grinding wheel 34 is rotated by a fluid motor 68 (see FIGS.1 and 2) about an axis 70 which extends perpendicular to and intersectsan axis 72 of the main dressing wheel 34 (FIG. 7). The motor 68accelerates the dressing wheel 34 to a predetermined speed before it isbrought into engagement with the shoulder surface 26 of the grindingwheel 28. The fluid motor 68 continues to rotate the dressing wheel 34about its axis 70 at the desired wheel dressing speed simultaneouslywith rotation of the grinding wheel 28 about its central axis 48 todress the shoulder surface 26 of the grinding wheel 28 in a knownmanner.

Once the shoulder surface 26 of the grinding wheel 28 has been dressedto the desired surface finish, the three-position motor assembly 42 isoperated from the fully extended condition of FIG. 5 to the retractedcondition of FIG. 3 to move the shoulder dressing wheel 34 to theretracted position of FIG. 11. At this time the shoulder dressing wheel34 and main dressing wheel 32 are both in the fully retracted or initialcondition of FIG. 6 and are spaced apart from the grinding wheel 28;Therefore, the dressing wheels 32 and 34 will not interfere with normaloperation of the grinding wheel 28. Although the main surface 24 of thegrinding wheel 28 has been shown as having a larger surface area thanthe shoulder 26, it is contemplated that under certain circumstances theshoulder 26 may have a greater surface area than the main surface 24.Depending upon the configuration of the parts to be finished by thegrinding machine 20, the grinding surfaces 24 and 26 could 'have aconfiguration other than the illustrated frustro-conical configurationand could have an angle of intersection other than the illustrated rightangle. It is also contemplated that under certain circumstances it'may-be desirable to simultaneously dress both the main surface 24 andshoulder surface 26 of the grinding wheel 28 with the two dressingwheels 32 and 34 rather than dressing them sequentially in the mannerillustrated schematically in FIGS. 6-11.

The three-position motor assembly 42 includes a cylinder assembly 74(see FIG. 3) which defines an operating chamber 76 having a relativelylarge diameter main portion 78 and a relatively small diameter secondaryportion 80. A pair of pistons 82 and 84 are fixedly interconnected at athreaded connection 88 and cooperate with a movable third piston 90. Thefixed piston elements 82 and 84 are connected with the wheel slide 38'by a suitable connection 94 and an outer'end of 'a piston rod 96.

When the motor assembly 42 is in the retracted condition of FIG. 3, anannular stop portion 100 of the piston 82 is disposed in abuttingengagement with an annular end face 102 of the movable piston 90. An endsurface 104 of the movable piston is disposed in abutting engagementwith a circular end wall 106 of the cylinder assembly 74. Passages 108connect a circular recess 1 10 within the movable piston 90 with apassage 112 extending through the cylinder assembly 74. It

should be noted that when the motor assembly 42 is in the retractedcondition of FIG. 3, an annular end surface 114 on the piston 84 isspaced from an annular inner surface 116 of the movable piston 90.

To operate the motor assembly 42 from the retracted condition of FIG. 3to the partially extended condition of FIG. 4, a solenoid SI-IA (seeFIG. 3) is energized to shift a valve spool 120 toward the right (asviewed in FIG. 3). This movement of the valve spool 120 ports fluidunder pressure through a valve passage 122 to a passage 124 through thecylinder 74 to a pressure chamber 126 formed between the piston elements82 and 90. The application of fluid pressure against an annularoperating or end surface 130 on the piston 82 causes the piston to moveleftwardly from the position shown in FIG. 3 to the position shown inFIG. 4. It-

should be noted that the fluid pressure in the chamber 126 is alsoapplied against the end face 102 of the movable piston 90 to press themovable piston firmly against the end surface 106 of the cylinderassembly 74. Therefore, when the annular end surface 114 of the pistonelement 84 engages the surface 116 on the piston 90, movement of thepiston 82 from the position shown in FIG. 4 is blocked. The cooperationbetween the movable piston 90 and the piston element 84 enables themotor assembly 42 to accurately position the wheel slide 38 with themain dressing wheel 32 in the position illustrated in FIGS. 1 and 7 toenable the dressing wheel 32 to dress the main surface 24 of thegrinding wheel 28.

When the motor assembly 42 is to be operated from the partially extendedcondition of FIG. 4 to the retracted condition of FIG. 3 to thereby movethe dressing wheel 32 through a wipe stroke, a solenoid SHB is energizedto shift the valve spool 120 toward the left (as viewed in FIG. 3). Thiscauses fluid under pressure to be ported through a valve passage 134 anda passage 136 of the cylinder assembly 74 to an operating chamber 138.The application of fluid pressure against an annular end face 140 of thepiston 82 moves the piston toward the right from the position shown inFIG. 4 to the position shown in FIG. 3. It should be noted that at thistime the chamber 1 is connected to drain through a valve spool 144 andthat the chamber 126 is connected to drain through the valve spool 120.

When the motor assembly 42 is to be operated from the retractedcondition of FIG. 3 to the fully extended condition of FIG. 5, asolenoid 8HB is energized to move the valve spool 144 toward the left(as viewed in FIG. 3). This ports fluid pressure through a valve passagel46 to the operating chamber 1 10. At this time the solenoids 511A andSHB are deenergized so that the operating chambers 126 and 138 areconnected with drain or reservoir through passages in the valve spool120. Therefore, the relatively high fluid pressure in the chamber 110causes the movable piston 90, piston 84 and piston 82 to move leftwardly(as viewed in FIG. 3) until the end face 102 of the piston 90 engages anannular stop surface 150 formed on a cylindrical wall of the cylinderassembly 74 (see FIG. 5). The fluid pressure in the operating chamber110 causes the piston 84 to continue moving until the surface 114' onthe piston element 84 engages the surface 116 on the piston 90. At thistime the motor assembly 42 is in the fully extended condition of FIG. 5and the shoulder dressing wheel 34 is in the postion shown .in FIG. 10.It should be noted that the stop' surface 150 accurately locates themovable piston 90 and that the engagement between the 6 surface 114 and116 on the pistons and 84 function to accurately position the dressingwheel slide 38 for a shoulder dressing operation.

When the shoulder surface 26 of the grinding wheel 28 has been dressed,the motor assembly 42 is operated from the fully extended condition ofFIG. 5 to the retracted condition of FIG. 3 to move the dressing wheel34 from the position shown in FIG. 10 to the position shown in FIG. 11.To accomplish this, the solenoid 8118 is deenergized and the valve spool144 is moved toward the right (as viewed in FIG. 3) under the influenceof a biasing spring 156 to connect the operating chamber with drain. Thesolenoid SHB is then energized to connect the operating chamber 138 withhigh pressure line 158 which is supplied with fluid under pressure froma pump 160 driven by a motor 162. The relatively high fluid pressure inthe chamber 136 moves the piston 82 toward the right (as viewed in FIG.5) to bring the stop portion 1 10 of the piston into abutting engagementwith the movable piston 90. Continued rightward movement of the piston82 moves the movable piston 90 away from the annular stop surface 150 tothe position shown in FIG. 3. The solenoid SHB is then deenergized andbiasing springs 166 and 168 center the valve spool 120 so that both ofthe operating chambers 126 and 138 are connected with drain.

Control circuitry 174 for effecting operation of the wheel dressingapparatus 22 through a dressing cycle is illustrated schematically inFIG. 12. When a wheel dressing cycle is to be undertaken, the motorassembly 42 and associated control valves are in the condition shown inFIG. 3. In addition, the base slide motor 46 is retracted as shown inFIG. 3 so that the main and shoulder dressing wheels 32 and 34 are inthe position illustrated schematically in FIG. 6. A switch 176 is closedto energize a motor 178 for driving the sheave 56 (FIG. 1) and maindressing wheel 32.

When a start button 180 (FIG. 12) is depressed to initiate the beginningof a wheel dressing cycle, a relay 182 is energized. Energization of therelay 182 closes holding contacts 184 to maintain the relay in anenergized condition even though the start 180 is released. Energizationof the relay 182 effects operation of a valve 186 (FIG. 3) to port fluidunder pressure through a valve passage 190 to the head end of the baseslide motor 46. This extends the motor 46 to move the base slide 40toward the grinding wheel 28 along a path extending perpendicular to theaxis of rotation of the grinding wheel. Thus, upon enerigzation of therelay 182, its normally open contacts 194 are closed to energize a 4H3solenoid and shift the valve spool 186 toward the left (as viewed inFIG. 3).

In addition to effecting operation of the base slide motor 46,energization of the relay 182 (FIG. 12) causes its normally opencontacts 196 to close and effect energization of the SHA solenoid.Energization of the 511A solenoid causes the valve spool 120 to beshifted toward the right (as viewed in FIG. 3) to port fluid underpressure to the operating chamber 126. This fluid pressure causes thepiston 82 to move from the retracted position of FIG. 3 to the partiallyextended position of FIG. 4 in the manner previously explained. Thecombined operation of the three-position motor assembly 42 and the baseslide motor 46 results in movement of the main dressing wheel 32 fromthe retracted position of FIG. 6 to the operating position of FIG. 7 inwhich the dressing wheel 32 is effective to dress the main surface 24 ofthe grinding wheel 28 in a 7 known manner.

When the main dressing wheel 32 is to be moved through a wipe strokefrom the position shown in FIG. 7 to the position shown in FIG. 8, awipe button 200 (FIG. 12) is manually actuated to energize a relay 202and initiate operation of a timer 204. Actuation of the relay 202 closesits normally open holding contacts 206. Simultaneously therewith,normally closed contacts 208 of the relay 202 are opened to deenergizethe solenoid SHA. Normally open contacts 212 of the relay 202 are closedto energize the solenoid SHB.

Energization of the solenoid SHB causes the valve spool 120 to shift tothe left from the position shown in FIG. 3 to port fluid under pressureto the operating chamber 138. The fluid pressure in the operatingchamber 138 is applied against the end face 140 of the piston 82 to movethe piston fromm the partially extended position of FIG. 4 to theretracted position of FIG. 3. This movement of the piston 82 is parallelto the main surface 24 and the axis of rotation 72 of the main dressingwheel 32. The movement of the piston 82 is transmitted to the dressingwheel slide 38 through the connection 94 to move the main dressing wheel32 across the main surface 24 of the grinding wheel 28 with a wipingaction.

The timer 204 times out after the elapse of a sufficient period of timemto enable the main dressing wheel 32 to move through the wiping stroke.When this occurs, normally closed timer contacts 216 and 218 and 220(FIG. 12) are opened. Opening of the timer contacts 216 deenergizes the4HB solenoid to enable a biasing spring 224 (see FIG. 3) to shift thevalve spool 186 back to the position shown in FIG. 3 in which fluid isported to the rod end of the base slide motor 46 to retract the slidemotor. This moves the base slide 40 away from the grinding wheel 28 toshift the dressing wheels 32 and 34 to the positions illustratedschematically in FIG. 9.

Opening of the timer contacts 218 and 220 interrupts the circuit forenergizing the relay 202 and the solenoid SHB. Deenergization of thesolenoid H8 allows the biasing springs 166 and 168 to shift the valvespool to the neutral position of FIG. 3. This connects the operatingchamber 126 and 138 of the now retracted motor assembly 42 with drain.If the shoulder surface is not to be dressed, a stop button 225 can beactuated at this time to interrupt the wheel dressing operation.

Assuming that the shoulder surface 26 is to be dressed, a shoulder grindbutton 228 is closed. This completes a circuit for energizing the 811Brelay to effect a shifting of the valve spool 144 toward the left (asviewed in FIG. 3). This movement of the valve spool 144 ports fluidunder pressure to the operating chamber 110 and effcts operation of themotor assembly 42 to the fully extended condition of FIG. 5. As themotor assembly 42 is extended, the shoulder dressing wheel 34 is movedradially toward the shoulder surface 26 along a path extendingperpendicular to the shoulder surface and parallel to the main surface24. It should be noted that upon previous actuation of the start switch180 and energization of the relay 182, contacts 232 of the relay 182 areclosed to effect energization of a 9118 solenoid (FIG. 3).

The previous energization of the 911B solenoid shifted a valve spool 236toward the left (as viewed in FIG. 3) against the influence of a biasingspring 238 to connect the dressing wheel drive motor 68 with fluid underpressure through a valve passage 240. The motor 68 quickly brings theshoulder dressing wheel 34 up to speed. Therefore as the motor assembly42 is operated from the retracted condition of FIG. 3 to the extendedcondition of FIG. 5, the rotating dressing wheel 34 is brought intoengagement with the shoulder surface 26 on the rotating grinding wheel28. When the shoulder surface 26 has been dressed, the shoulder grindbutton 228 is released and the solenoid 811B is deenergized. Thisenables a biasing spring 156 to shift the valve spool 144 back to theposition shown in FIG. 3 in which the chamber is connected with drain.

After the main and shoulder surfaces 24 and 26 on the grinding wheel 28have been dressed, the stop button 225 is actuated. Actuation of thestop button 225 interrupts the circuit for energizing the relay 182 sothat its normally open holding contacts 184 are opened. In addition,contacts 232 of the relay 182 are open to deenergize the solenoid 911Bso that the valve spool 236 is returned to the position illustrated inFIG. 3 by the biasing spring 238. This interrupts the flow of fluid tothe motor 68 and rotation of the shoulder dressing wheel 34.

As the stop button 225 is actuated, a circuit to energize a relay 254 iscompleted. Energization of the relay 254 closes its contacts 256 tocomplete a circuit for energizing SHB solenoid. Energization of the SHBsolenoid causes the valve spool to be shifted to the left (as viewed inFIG. 3) to port fluid under pressure to the operating chamber 138. Thiscauses the motor assembly 142 to be returned to the retracted conditionof FIG. 3. In addition, operation of the relay 254 activates a resetcircuit (not shown) for the timer 204 to reset it for the next dressingoperation. When the stop button 225 is released, the circuit forenergizing the relay 254 is opened and the circuitry 174 is in conditionfor the next dressing operation.

The control circuitry 174 has been simplified in FIG. 12 in order toavoid prolixity of description. It is contemplated that the actualcontrol circuitry utilized with the wheel dressing apparatus 22 willinclude suitable interlocks and other cirduit refinements. It shouldalso be understood that if desired timers, similar to the timer 204, canbe provided for the wipe cycles and the shoulder grind cycles. Ifdesired, suitable gauges and surface condition detecting devices of aknown construction could be utilized in association with the wheeldressing apparatus 22 to facilitate dressing the grinding wheel 28 to apredetermined finished condition.

m view of the foregoing description, it can be seen that wheel dressingapparatus 22 includes a main deresing wheel 32 for dressing a mainsurface 24 of the grinding wheel 28 and a shoulder dressing wheel 34 fordressing the shoulder surface 26 of the grinding wheel 28. The twodressing wheels 32 and 34 are mounted on a common slide 38 which ismoved under the combined influence of the base slide motor 46 andthree-position motor assembly 42. The three-psotti motor assembly 42enables the dressing wheel slide 38 to be accurately positioned with thedressing wheels 32 and 34 in either the retracted position of FIG. 6,the main surface grinding position of FIG. 7, or the shoulder surfacegrinding position of FIG. 10.

. wheels 32 and 34 have cylindrical surfaces 52 and 64 which areutilized to dress the main and shoulder surfaces 24 and 26 of thegrinding wheel 28, the area of contact between the dressing wheels andthe surfaces of the grinding wheel 28 are minimized with a resultingenhancing of the finish on the dressed grinding wheel 28 and aminimizing of the pressure which must be applied against the dressingwheels 32 and 34 to dress the grinding wheel.

Having described a specific preferred embodiment of the invention thefollowing is claimed:

1. A method of dressing the periphery of a rotatable grinding wheelhaving a circular main surface which extends at an acute angle to theaxis of rotation of the grinding wheel and a circular shoulder surfaceextending transversely to the main surface, said method comprising thesteps of rotating the grinding wheel, moving a first rotatable dressingwheel into engagement with the main surface of the rotating grindingwheel, said step of moving the first dressing wheel into engagement withthe main surface of grinding wheel includes the step of moving the firstdressing wheel along a first path which intersects the main surface onthe grinding wheel, said first path extending substantiallyperpendicular to the axis of rotation of the grinding wheel and at anacute angle to the axis of rotation of the first dressing wheel toprovide for engagement of the first dressing wheel with the main surfaceof the grinding wheel as the first dressing wheel is moved along thefirst path, rotating the first dressing wheel about a first axisextending generally parallel to the main surface of the grinding wheelwhen the first dressing wheel is in engagement with the main surface ofthe grinding wheel, moving the first dressing whee] away from the mainsurface of the grinding wheel after the main surface has been dressed,moving a second dressing wheel into engagement with the shoulder surfaceof the rotating grinding wheel after performing said step of moving thefirst dressing wheel away from the main surface of the grinding wheel,said step of moving the second dressing wheel into engagement with theshoulder surface of the grinding wheel including the step of moving thesecond dressing wheel along a second path extending transversely tothe-first path, rotating the second dressing wheel about a second axisextending generally parallel to the shoulder surface of the grindingwheel and transversely to said first axis when the second dressing wheelis in engagement with the shoulder surface of the grinding wheel, andmoving the second dressing wheel away from the shoulder surface of thegrinding wheel after the shoulder surface of the grinding wheel has beendressed.

2. A method as set forth in claim 1 further including the step of wipingthe main surface of the grinding wheel by moving'the first dressingwheel axially along a path extending parallel to the main surface of thegrinding wheel.

3. A method as set forth in claim 1 wherein said step of moving thefirst dressing wheel into engagement with the main surface of thegrinding wheel includes moving the first dressing wheel through a firstdistance along said first axis and said step of moving the seconddressing wheel into engagement with the shoulder surface of the grindingwheel includes moving the first dressing wheel through a second distancealong said first axis, said second distance being greater than saidfirst distance.

4. A method as set forth in claim 1 wherein said step of moving thefirst dressing wheel into engagement with the main surface of thegrinding wheel includes moving the first dressing wheel radially alongthe first path and said step of moving the second dressing wheel intoengagement the shoulder surface of the grinding wheel includes movingthe second dressing wheel radially along the second path.

5. A method as set forth in claim 1 wherein said step of moving thefirst dressing wheel along the first path includes the step of movingthe second dressing wheel along the first pa'th with the first dressingwheel, said step of moving the second dressing wheel along the secondpath includes the step of moving the first dressing wheel along thesecond path with the second dressing wheel.

1. A method of dressing the periphery of a rotatable grinding wheelhaving a circular main surface which extends at an acute angle to theaxis of rotation of the grinding wheel and a circular shoulder surfaceextending transversely to the main surface, said method comprising thesteps of rotating the grinding wheel, moving a first rotatable dressingwheel into engagement with the main surface of the rotating grindingwheel, said step of moving the first dressing wheel into engagement withthe main surface of grinding wheel includes the step of moving the firstdressing wheel along a first path which intersects the main surface onthe grinding wheel, said first path extending substantiallyperpendicular to the axis of rotation of the grinding wheel and at anacute angle to the axis of rotation of the first dressing wheel toprovide for engagement of the first dressing wheel with the main surfaceof the grinding wheel as the first dressing wheel is moved along thefirst path, rotating the first dressing wheel about a first axisextending generally parallel to the main surface of the grinding wheelwhen the first dressing wheel is in engagement with the main surface ofthe grinding wheel, moving the first dressing wheel away from the mainsurface of the grinding wheel after the main surface has been dressed,moving a second dressing wheel into engagement with the shoulder surfaceof the rotating grinding wheel after performing said step of moving thefirst dressing wheel away from the main surface of the grinding wheel,said step of moving the second dressing wheel into engagement with theshoulder surface of the grinding wheel including the step of moving thesecond dressing wheel along a second path extending transversely to thefirst path, rotating the second dressing wheel about a second axisextending generally parallel to the shoulder surface of the grindingwheel and transversely to said first axis when the second dressing wheelis in engagement with the shoulder surface of the grinding wheel, andmoving the second dressing wheel away from the shoulder surface of thegrinding wheel after the shoulder surface of the grinding wheel has beendressed.
 2. A method as set forth in claim 1 further including the stepof wiping the main surface of the grinding wheel by moving the firstdressing wheel axially along a path extending parallel to the mainsurface of the grinding wheel.
 3. A method as set forth in claim 1wherein said step of moving the first dressing wheel into engagementwith the main surface of the grinding wheel includes moving the firstdressing wheel through a first distance along said first axis and saidstep of moving the second dressing wheel into engagement with theshoulder surface of the grinding wheel includes moving the firstdressing wheel through a second distance along said first axis, saidsecond distance being greater than said first distance.
 4. A method asset forth in claim 1 wherein said step of moving the first dressingwheel into engagement with the main surface of the grinding wheelincludes moving the first dressing wheel radially along the first pathand said step of moving the second dressing wheel into engagement withthe shoulder surface of the grinding wheel includes moving the seconddressing wheel radially along the second path.
 5. A method as set forthin claim 1 wherein said step of moving the first dressing wheel alongthe first path includes the step of moving the second dressing wheelalong the first path with the first dressing wheel, said step of movingthe second dressing wheel along the second path includes the step ofmoving the first dressing wheel along the second path with the seconddressing wheel.